Wide version of ThumbKey (#889)

This is a layout based on the philosophy of the default ThumbKey layout,
but designed for more efficient use with two hands.

- Vowels on the right, common consonants on the left.
- The most common letters are presses (not swipes), and are sorted so
  that the most common letters are at the sides and lower down.
- Secondary letters are often chosen to relate to the primary letter on
  the key (eg: "m" is paired with "n").
- originally "f" and "k" were the other way around, but this way felt
  more natural - and "k" is often paired with consonants, while "f" is
  usually next to a vowel (or itself).
- Having more than four swipes on a key was avoided as much as possible,
  because 8-way swipes are harder to get the swipe direction correct on.
- In fact, the letter mode minimises swipes altogether. This leaves
  plenty of space for, eg, putting various "A" diacritics on the "A"
  key in other keyboards based on this one.
- The central key on the letter board has a selection of symbols - I
  picked the ones I thought were most likely to be used frequently in
  runs of words (note that I replaced * with ", compared to the original
  ThumbKey layout).
- The numeric keyboard prioritises putting the numbers in a classic
  phone layout over maximising access for two hands. Similarly, * and #
  are swipes towards where those symbols would be on a phone keypad.
- It also aims to lay similar symbols out next to each other, rather
  than sorting by frequency - this is because this mode is used much
  less frequently, so it's harder to learn where symbols are, and so I
  prioritised making searching for them easier. For example, all the
  "pause" puncutation (comma, full stop, semi-colon, colon, exclamation,
  question) are on the 5 key or the bottom of the 2 key, and superscript
  marks like quotation marks are on the 6 key. Key 7 has "mathematical
  symbols". Key 4 has currency. All the types of brackets are likewise
  grouped together (opening on the left and closing on the right).
- The central key on the numeric board has the same swipes as the
  central key on the letter board to leverage the habits learnt in the
  letter mode.
- If symbols are mirrors of each other, I tried to mirror them in the
  layout.

Co-authored-by: Alex Merry <[email protected]>